This invention relates generally to clamps for use in regulating fluid flow rate through plastic tubing and more specifically to a self-contained device for regulating the fluid flow therethrough.
Plastic tubing, generally of a PVC, or vinyl material is extensively employed in hospitals as a fluid conduit in numerous applications. Vinyl tubing is inexpensive and generally inert so as to be advantageous for administering fluids to a patient such as in parenteral solution administration sets. Numerous devices such as cam, screw and roller type clamps are available for regulating the fluid flow rate of the solution reaching the patient by selectively compressing the tubing to vary the size of the fluid lumen. These flow regulating devices are positioned along the length of tubing to permit the operator to regulate the flow rate and the volume per unit time of liquid administered to a particular patient.
When vinyl tubing is compressed, its inherent rigidity produces a high internal strain to resist compression for the first several minutes after being clamped. Eventually, the tubing will begin to relieve its internal strain or undergo the phenomena of "cold flow" causing a progressive change in the cross-sectional area of the constricted tubing producing a potentially dangerous fluctuation in the desired flow rate. Consequently, these prior devices must be frequently monitored and re-adjusted to maintain a prescribed flow rate.
Although all of the types of clamps referred to above regulate flow by compressing the tubing, they are entirely dissimilar in operation and effectiveness. Cam-type clamps generally employ a transaxial cam to compress a particular transverse section of tubing, but are generally difficult for the attendent or nurse to manipulate and their configurations do not readily lend themselves to variable settings of flow regulation. Screw clamps have a threaded plunger to selectively compress the tubing beneath the plunger by which to regulate flow. However, screw clamps are notoriously unreliable in maintaining a set flow rate due to the formation of secondary lumens around the plunger caused by cold flow. Generally, the plunger cannot completely crimp the tubing closed to block flow for any length of time due to the increased tendency for the formation of secondary lumens on either side of the plunger.
Roller clamps have heretofore generally had a U-shaped body to fit over the tubing with a roller mounted therein to selectively compress the tubing against the base of the body. The early roller clamps, such as shown in U.S. Pat. No. 3,189,038, suffered a severe drawback from cold flow by providing a flat-inclined clamping surface relative to the movement of the roller to progressively compress the tubing in a uniform transverse cross-section against the compression surface which lead to secondary lumen formation.
In an attempt to overcome the difficulties with cold flow produced by a flat compression surface several roller clamps have been proposed with a grooved clamping surface. One such clamp compresses the transverse edges of the tubing by a roller mounted uniformly above a compression surface which has a channel of varying cross-section to control the lumen size. For example, U.S. Pat. No. 3,685,787 discloses a clamp having a roller spaced uniformly above a compression surface to squeeze the transverse edges of the tubing while permitting the central portion of the tube to flow into a longitudinal channel in the compression surface to form a lumen. The channel varies in depth from large to small to regulate lumen size. Although that device was an improvement over earlier roller clamps, the configuration and cross-sectional area of the channel still permitted "cold flow" migration of the compressed tubing wall into the excess channel space causing fluctuations in the desired flow rate. U.S. Pat. Nos. 4,031,263 and 4,047,694 disclose improvements to the embodiment of the 3,685,787 patent in an attempt to direct the cold flow away from the excess space in the channel and a recessed roller to permit migration of the tubing during cold flow into this additional space and away from flow-rate defining lumen. However, these and the other prior art roller clamps have not adequately overcome the disadvantages attributed to cold flow making the currently available roller clamps less than satisfactory.
To overcome some of these difficulties, the use of a cam-type clamp with an expensive and complicated multi-lumen insert of resilient material which does not exhibit the phenomena of cold flow when compressed, has been suggested in U.S. Pat. No. 3,805,830 to alleviate flow rate fluctuations attributed to cold flow and capillary action encountered with standard vinyl tubing. The patentee of U.S. Pat. No. 3,948,977 has proposed that the multi-lumen insert described therein may be employed with the screw clamp disclosed in U.S. Pat. No. 3,805,830. This screw clamp device suffers from the disadvantages of limited control range and difficulty of complete shut-off inherent with that type of clamp. Both of these clamps employing the resilient insert are subject to flow rate variations produced by tugging or stretching of the administration tubing by external forces. For example, movement by the patient which produced a pulling force would tend to change the flow rate due to the resilient, easily stretched insert making these devices unreliable for maintaining consistent flow rates.
Heretofore, the prior tubing clamps have failed to overcome flow rate fluctuations attributed to cold flow and/or external stretching forces causing them to be unsatisfactorily unreliable for failing to maintain a prescribed flow rate.